1. Field of the Invention
This invention relates to woven fabric laminates having superior resistance to penetration by ballistic projectiles, assemblies thereof, and the method by which they are made.
2. Description of the Related Art
The construction of body armor for personal protection is an ancient but not archaic art. The origin and first use of armor likely dates to pre-historic ages Metal armor was already well known to the Egyptians by 1500 B.C.E. A wall painting in a tomb dating from the reign of Amenhotep II (1436-1411 B.C.E.) clearly shows a defensive garment formed of overlapping bronze scales. These were sewn to a cloth backing resembling a long shirt with short sleeves and an opening for the neck. (“A Historical Guide to Arms and Armor”, Steven Bull, Edited by Tony North, Studio Editions Ltd., London, 1991)
The use of body armor persisted until about the end of the 17th century. Armor had increased in weight in order to remain effective against musket fire. However, at the same time, new strategy and tactics called for greater infantry mobility. Armor fell into disuse and was not widely used again until World War II. When during World War II, casualties from shell fragments rose to 80%, and, with 70% of all wounds affecting the torso, it became highly desirable to produce a suitable body armor. Armor for bomber crews and ground troops was developed of steel, aluminum and resin-bonded fiber glass plates, as well as of heavy nylon cloth.
In more recent years, with the introduction of new strong fibers such as aramids and high molecular weight polyethylene, the weight of body armor was reduced to a level where it became practical for daily use by civilian police officers. In 1974, there were 132 federal, state and local officers killed in the line of duty; 128 of them were slain with firearms, and most of the murder weapons were handguns of 0.38 caliber or less. Lightweight body armor was introduced soon afterward. It has been credited with preventing the death of an estimated 2,500 law officers in the ensuing years (Selection and Application Guide to Personal Body Armor by the National Institute of Justice, November 2001).
Various constructions are known for fiber-reinforced composites used in impact and ballistic resistant articles such as helmets, panels, and vests. These composites display varying degrees of resistance to penetration by high speed impact from projectiles such as BB's, bullets, shells, shrapnel, glass fragments and the like. For example, U.S. Pat. Nos. 6,268,301 B1, 6,248,676 B1, 6,219,842 B1; 5,677,029, 5,587,230; 5,552,208, 5,471,906; 5,330,820; 5,196,252; 5,190,802; 5,187,023; 5,185,195; 5,175,040; 5,167,876; 5,165,989; 5,124,195; 5,112,667; 5,061,545; 5,006,390; 4,953,234; 4,916,000; 4,883,700; 4,820,568; 4,748,064; 4,737,402; 4,737,401, 4,681,792; 4,650,710, 4,623,574; 4,613,535; 4,584,347; 4,563,392; 4,543,286; 4,501,856; 4,457,985; and 4,403,012; PCT Publication No. WO 91/12136; and a 1984 publication of E.I. DuPont De Nemours International S.A. entitled “Lightweight Composite Hard Armor Non Apparel Systems with T-963 3300 dtex DuPont Kevlar 29 Fibre”, all describe ballistic resistant composites which include high strength fibers made from materials such as high molecular weight polyethylene, aramids and polybenzazoles. Such composites are said to be either flexible or rigid depending on the nature of their construction and the materials employed.
U.S. Pat. No. 4,737,401, Harpell et al., filed Dec. 9, 1985, and commonly assigned, discloses ballistic resistant fine weave fabric articles.
U.S. Pat. No. 4,623,574, Harpell et al., filed Jan. 14, 1985, and commonly assigned, discloses simple composites comprising high strength fibers embedded in an elastomeric matrix.
U.S. Pat. No. 5,677,029, Prevorsek et al., filed Dec. 12, 1996, and commonly assigned, discloses a flexible penetration resistant composite comprising at least one fibrous layer comprised of a network of strong fibers, and at least one continuous polymeric layer coextensive with, and at least partially bound to a surface of one of the fibrous layers.
U.S. Pat. No. 5,552,208, Lin et al, filed Oct. 29, 1993, and commonly assigned, discloses a ballistic resistant article comprised of a high strength fiber network in a matrix and a second matrix material in the form of a film which is adjacent to at least one side of the matrix-impregnated fiber network.
U.S. Pat. No. 5,471,906, Bachner, Jr. et al., discloses a body armor comprising an armor layer and a cover, surrounding and sealing the armor layer, comprising a sheet of waterproof and moisture vapor permeable fabric oriented to face the wearer.
U.S. Pat. Nos. 5,788,907 and 5,958,804, Brown, Jr. et al., disclose ballistically resistant calendered fabrics.
Aramid fabrics rubber coated on one or both sides are commercially produced by Verseidag Industrietextilien Gmbh. under the product name UltraX. Rigid panels formed by bonding the rubber-coated fabrics together under heat and pressure are also available.
Ballistically resistant composites are typically formed from layers of woven fabrics or sheets of fibers which are plied together. The fibers in a sheet may be unidirectionally oriented or felted in random orientation. Where the individual plies are unidirectionally oriented fibers, the successive plies are rotated relative to one another, for example at angles of 0°/90° or 0°/45°/90°/45°/0° or at other angles. In previous processes, with some exceptions, the individual plies of woven fabrics or fibers have generally been uncoated, or embedded in a polymeric matrix material which filled the void spaces between the fibers. If no matrix was present, the fabric or fiber sheet was inherently flexible. A contrasting type of construction is a composite consisting of fibers and a single major matrix material. To construct rigid composites of this type, individual plies were bonded together using heat and pressure to adhere the matrix in each ply, forming a bond between them, and consolidating the whole into a unitary article.
Each of the constructions cited above represented progress toward the goals to which they were directed. However, none described the specific constructions of the laminates and assemblies of this invention and none satisfied all of the needs met by this invention.
These earlier constructions had several disadvantages. Woven fabrics generally had poorer ballistic resistance than cross-plied unidirectional fiber composites. On the other hand, woven fabrics could be produced at lower cost and greater ease of manufacture with more commonly available equipment than cross-plied unidirectional fiber composites. The ballistic resistance of woven fabrics was improved by incorporation of a low modulus elastomeric matrix. However, the use of a matrix resin which completely filled the void spaces between the fibers added to the weight of the fabric and decreased its flexibility. A need exists for a woven fabric construction that retains the advantages of lower cost and greater ease of manufacture compared to cross-plied unidirectional composites, but which has ballistic resistance superior to conventional fabrics. Ideally, the woven fabric construction is of high flexibility but may be bonded to itself, or to hard facings, to form rigid panels.